It won't change the price of the fetchlands that much - they are still heavily played in legacy, commander etc - but it will change the price of the decks. A lot of decks use 8-12 fetchlands and so, it could reduce the price of a deck by anywhere from $40-$500 depending of the deck, which could bring in new players with less income.
However, what it will do is change the metagame. Some decks are punished a lot more by the reduction to 4 fetch lands than others. Humans and Tron run hardly any fetch lands and so won't be affected, but Jund and Jeskai control run a tonne and so might have to cut colours for consistency, and
Death's Shadow might not even be possible. Since Tron and Humans are already dominant decks, this could make the format more restrictive.
But, hey, who knows.